Operation and performance of a fuel injector may change over a life time of a fuel injector. Further, one fuel injector may operate unlike a different but same type of fuel injector due to piece-to-piece variability. Even though one fuel injector may operate slightly different from other fuel injectors, it may be possible to operate other fuel injectors in a way that allows each fuel injector to deliver a desired amount of fuel. One way to characterize operation of a fuel injector is to raise pressure in a fuel rail, deactivate a fuel pump, inject fuel while monitoring pressure in the fuel rail, and combust the fuel. A pressure drop in the fuel rail may be correlated to an amount of fuel injected by the fuel injector and a characterization of fuel flow and injector opening time may be adjusted responsive to the fuel pressure drop. While such a method provides for active fuel injector characterization, it allows fuel injectors to be re-characterized only for fuel injector operating regions that are activated when the re-characterization is performed so that engine emissions and performance do not degrade. For example, if the engine is operating at 0.5 load and fuel flow is X gram per intake stroke to operate the engine at stoichiometric combustion, only fuel injector operation for 0.5 load and stoichiometric combustion may be re-characterized while operating the engine at 0.5 load. As a result, it may take a long time to fully characterize a fuel injector. Further, the engine may have to operate without its fuel injectors being re-characterized for a period of time, which may result in engine air-fuel ratio errors.
The inventors herein have recognized the above-mentioned issues and have developed a method for operating an engine, comprising: increasing pressure of a fuel rail to a threshold pressure and deactivating a cylinder of the engine in response to entering deceleration fuel shut-off; deactivating a fuel pump in response to pressure in the fuel rail being at the threshold pressure; injecting fuel to the deactivated cylinder; correlating pressure drop in the fuel rail to injector operation; and operating a fuel injector responsive to the correlation.
By characterizing operation of a fuel injector during deceleration fuel shut-off (DFSO), it may be possible to re-characterize fuel injector operation over a wide range of fuel injection amounts so that fuel injector operation may be corrected without having to first operate the engine at conditions where fuel injector operation has not been characterized. In addition, injecting fuel while engine cylinders are deactivated in response to entering a deceleration fuel shut-off mode may act to keep constituents in a catalyst coupled to the engine balanced so that exhaust gases may be converted efficiently.
The present description may provide several advantages. In particular, the approach may improve fuel injector characterization by allowing fuel injectors to be characterized for fuel injection amounts that are not based on a present engine air flow rate. In addition, the method allows for adjusting an engine air flow rate while the engine is in a deceleration fuel shut-off mode so that fuel injectors may be characterized sooner after entering deceleration fuel shut-off. Further, the approach adjusts fuel injected during deceleration fuel shut-off with oxygen stored in a catalyst so that the possibility of hydrocarbons breaking through the catalyst may be reduced while fuel injectors are being characterized. Further still, since fuel injector characterization is performed during DFSO, pressure noise do to other fuel injectors injecting fuel may be eliminated.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.